Quick, Simple Macro Solution. The Hoya 82mm HMC Diopter Filter (+4) optically decreases your lens’s focal length, which in turn lessens the minimum focusing distance between the lens and your subject. This filter gives you a 9.8-inch focal length. The end result? A macro solution that doesn’t require a macro lens.

High-Quality Construction. This filter has three layers of anti-reflection coating on each side of its chemically hardened optical glass to ensure maximum clarity while preventing internal ghosting and, naturally, reflections. This filter provides roughly 97% average light transmission, and features a durable, lightweight aluminum-alloy filter ring.

About Diopters and Underwater Photography. When you take a camera and lens underwater behind a dome, your camera sees a virtual image that’s created by the light rays passing from the water into air through the dome. The image is at a fixed location in relation to the camera sensor—about 12 inches (30.5 cm) away—regardless of the distance of your subject from the sensor. A diopter changes the focal distance of your lens to a fixed value. The focal length of a +4 diopter is 9.8 inches (250mm), which happens to hit the sweet spot when shooting behind a dome port underwater.